The Alfvénic nature of chromospheric swirls

Battaglia, Andrea Francesco; Cuissa, José Roberto Canivete; Calvo, Flavio; Bossart, Aleksi; Steiner, O.

doi:10.1051/0004-6361/202040110

Cited by 35 publications

(65 citation statements)

References 56 publications

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“…2). Rotational motions have also been found in simulations by Wedemeyer-Böhm et al (2012); Moll et al (2012); Shelyag et al (2013); Yadav et al (2020b); Battaglia et al (2021). The Poynting flux is injected into the coronal loop from both footpoints.…”

Section: Poynting Flux and Heatingmentioning

confidence: 61%

A solar coronal loop in a box: Energy generation and heating

Breu,

Peter,

Cameron

et al. 2021

Preprint

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Context. Coronal loops are the basic building block of the upper solar atmosphere as seen in the extreme UV and X-rays. Comprehending how these are energized, structured, and evolve is key to understanding stellar coronae.Aims. Here we investigate how the energy to heat the loop is generated by photospheric magneto-convection, transported into the upper atmosphere, and how the internal structure of a coronal magnetic loop forms. Methods. In a 3D magnetohydrodynamics (MHD) model, we study an isolated coronal loop rooted with both footpoints in a shallow layer within the convection zone using the MURaM code. To resolve its internal structure, we limited the computational domain to a rectangular box containing a single coronal loop as a straightened magnetic flux tube. Fieldaligned heat conduction, gray radiative transfer in the photosphere and chromosphere, and optically thin radiative losses in the corona were taken into account. The footpoints were allowed to interact self-consistently with the granulation surrounding them.Results. The loop is heated by a Poynting flux that is self-consistently generated through small-scale motions within individual magnetic concentrations in the photosphere. Turbulence develops in the upper layers of the atmosphere as a response to the footpoint motions. We see little sign of heating by large-scale braiding of magnetic flux tubes from different photospheric concentrations at a given footpoint. The synthesized emission, as it would be observed by the Atmospheric Imaging Assembly (AIA) or the X-ray Telescope (XRT), reveals transient bright strands that form in response to the heating events. Overall, our model roughly reproduces the properties and evolution of the plasma as observed within (the substructures of) coronal loops.Conclusions. With this model we can build a coherent picture of how the energy flux to heat the upper atmosphere is generated near the solar surface and how this process drives and governs the heating and dynamics of a coronal loop.

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Section: Poynting Flux and Heatingmentioning

confidence: 61%

A solar coronal loop in a box: Energy generation and heating

Breu,

Peter,

Cameron

et al. 2021

Preprint

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“…Therefore, the dominance of the horizontal electromagnetic energy flux does not imply a lower vertical energy flow. In a recent study Battaglia, Andrea Francesco et al (2021) indicated that the upper photosphere and chromospheric swirls can provide a positive energy input.…”

Section: Discussionmentioning

confidence: 99%

“…Besides playing an essential role in generating an upwards pointing Poynting flux, the small-scale vortices could provides enough energy to heat the chromosphere (Yadav et al 2020). The swirling motions in the chromosphere also provides a mean net upwardly directed Poynting flux and can spatially correlate to intense vertical Poynting flux distributions (Battaglia, Andrea Francesco et al 2021). In active regions, a strong correlation between the averaged X-ray brightness and a proxy for Poynting flux was first suggested by Fisher et al (1998).…”

Section: Introductionmentioning

confidence: 99%

The importance of horizontal Poynting flux in the solar photosphere

Silva,

Murabito,

Jafarzadeh

et al. 2022

Preprint

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The electromagnetic energy flux in the lower atmosphere of the Sun is a key tool to describe the energy balance of the solar atmosphere. Current investigations on energy flux in the solar atmosphere focus primarily on the vertical electromagnetic flux through the photosphere, ignoring the Poynting flux in other directions and its possible contributions to local heating. Based on a realistic Bifrost simulation of a quiet-Sun (coronal hole) atmosphere, we find that the total electromagnetic energy flux in the photosphere occurs mainly parallel to the photosphere, concentrating in small regions along intergranular lanes. Thereby, it was possible to define a proxy for this energy flux based on only variables that can be promptly retrieved from observations, namely, horizontal velocities of the small-scale magnetic elements and their longitudinal magnetic flux. Our proxy accurately describes the actual Poynting flux distribution in the simulations, with the electromagnetic energy flux reaching 10 10 erg cm −2 s −1 . To validate our findings, we extended the analysis to SUNRISE/IMaX data. First, we show that Bifrost realistically describes photospheric quiet-Sun regions, as the simulation presents similar distributions for line-of-sight magnetic flux and horizontal velocity field. Second, we found very similar horizontal Poynting flux proxy distributions for the simulated photosphere and observational data. Our results also indicate that the horizontal Poynting flux in the observations is considerably larger than the vertical electromagnetic flux from previous observational estimates. Therefore, our analysis confirms that the electromagnetic energy flux in the photosphere is mainly horizontal and is most intense in localized regions along intergranular lanes.

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“…These new results have drawn renewed interest in wave heating mechanisms, both observationally and theoretically. Combinations of MHD wave aspects, vortices and null point ingredients have only been studied to some extent (McLaughlin et al 2011;Thurgood & McLaughlin 2013;Shelyag et al 2013;Mumford et al 2015;Tarr et al 2017;Tarr & Linton 2019;McLaughlin et al 2019;Liu et al 2019;Tziotziou et al 2020;Battaglia et al 2021). Because vortex flows, resulting torsional Alfvén waves and localized null points are so common, their co-occurrence is quite likely, opening up new challenges in the study of wave and energy propagation.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional MHD wave propagation near a coronal null point: a new wave mode decomposition approach

Yadav,

Keppens,

Braileanu

2022

Preprint

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Context. Ubiquitous vortex flows at the solar surface excite magnetohydrodynamic (MHD) waves that propagate to higher layers of the solar atmosphere. In the solar corona, these waves frequently encounter magnetic null points. The interaction of MHD waves with a coronal magnetic null in realistic 3D setups requires an appropriate wave identification method. Aims. We present a new MHD wave decomposition method that overcomes the limitations of existing wave identification methods. Our method allows to investigate the energy fluxes in different MHD modes at different locations of the solar atmosphere as waves generated by vortex flows travel through the solar atmosphere and pass near the magnetic null. Methods. We use the open-source MPI-AMRVAC code to simulate wave dynamics through a coronal null configuration. We apply a rotational wave driver at our bottom photospheric boundary to mimic vortex flows at the solar surface. To identify the wave energy fluxes associated with different MHD wave modes, we employ a wave-decomposition method that is able to uniquely distinguish different MHD modes. Our proposed method utilizes the geometry of an individual magnetic field-line in 3D space to separate out velocity perturbations associated with the three fundamental MHD waves. We compare our method with an existing wave decomposition method that uses magnetic flux surfaces instead. Over selected flux surfaces, we calculate and analyze temporally averaged wave energy fluxes, as well as acoustic and magnetic energy fluxes. Our wave decomposition method allows us to estimate the relative strengths of individual MHD wave energy fluxes. Results. Our method for wave identification is consistent with previous flux-surface-based methods and gives expected results in terms of wave energy fluxes at various locations of the null configuration. We show that ubiquitous vortex flows excite MHD waves that contribute significantly to the Poynting flux in the solar corona. Alfvén wave energy flux accumulates on the fan surface and fast wave energy flux accumulates near the null point. There is a strong current density buildup at the spine and fan surface. Conclusions. The proposed method has advantages over previously utilized wave decomposition methods, since it may be employed in realistic simulations or magnetic extrapolations, as well as in real solar observations, whenever the 3D fieldline shape is known. The essential characteristics of MHD wave propagation near a null, such as wave energy flux accumulation and current buildup at specific locations, translate to the more realistic setup presented here. The enhancement in energy flux associated with magneto-acoustic waves near nulls may have important implications in the formation of jets and impulsive plasma flows.

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The Alfvénic nature of chromospheric swirls

Cited by 35 publications

References 56 publications

A solar coronal loop in a box: Energy generation and heating

A solar coronal loop in a box: Energy generation and heating

The importance of horizontal Poynting flux in the solar photosphere

Three-dimensional MHD wave propagation near a coronal null point: a new wave mode decomposition approach

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